## combinat:-subset with a chosen number of elements?...

Hello

I need to test a huge amount of subsets and for doing that I was thinking of using combinat:-subset, since it avoids allocating memory for all subsets.  The problem with subset for my specific application is that it generates sets with all possible sizes and I just need subsets with a chosen number of elements.  Can that be done in maple?

Many thanks

Ed

## How to translate "blank pattern" to maple? ...

Hello

Moving from Mathematica to Maple and back these couple of days is driving me insane.  I get stuck trying to translate very simple things for not knowing each command belongs to each software.  Therefore I do apologize for another silly question.

Given the list of indexed variables

`varA := [A[1, 0], A[1, 1], A[1, 2], A[1, 3], A[1, 4], A[1, 5], A[1, 6], A[1, 7], A[1, 8], A[1, 9], A[2, 0], A[2, 1], A[2, 2], A[2, 3], A[2, 4], A[2, 5], A[2, 6], A[2, 7], A[2, 8], A[2, 9], A[3, 0], A[3, 1], A[3, 2], A[3, 3], A[3, 4], A[3, 5], A[3, 6], A[3, 7], A[3, 8], A[3, 9]]`

how to apply the following substitution

```varA/. {Subscript[A, m_, 2] -> Subscript[B, m, 3],
Subscript[A, m_, 3] -> Subscript[B, m, 2],
Subscript[A, m_, 5] -> Subscript[B, m, 6],
Subscript[A, m_, 6] -> Subscript[B, m, 5],
Subscript[A, m_, 7] -> Subscript[B, m, 9],
Subscript[A, m_, 9] -> Subscript[B, m, 7]}```

After trying a couple of commands such as map, subs, etc. I decide to try fromMma but no avail.

Many thanks for the patience and help.

Ed

## How can I improve a plot in Maple?...

Hello every one:

I am trying to plat the graph of a function (which has been defined in my code). I use the plat 3D operator but it doesn't give me the correct plot . I even increase the digites and numpoints but appearently it gave me less precise plot .

The problem of plots is as follows :

First I defined the function V and  asking maple to compute the values of V at some random points, spacially at (0,0) , (0,2*Pi) and (2*Pi,0) . It gave me 0 which means Maple computes the values correctly because it can be mathematically proved  that this function has the value 0 on all the board of a triangle with vertices (0,0) , (0,2*Pi) and (2*Pi,0) .

As you can see in my code maple doesn't show the correct value (0)  for the boundary points even at (0,0) !

I don't know how shoud I fix this problem.You can find my code in attached .Thanks in advanced for your help. Maple_question.mw

## How to extract the index of an indexed variable?...

Hello

I have lots of lists of indexed variables (I am not sure if that is the correct name for it. Please correct me if it is not).  One example is (length of the list can change as well as the indices of the variables):

`ans1 := [alpha[3, 7], alpha[3, 8], alpha[3, 9]]`

and I need to retrieve two lists from it:  1) [3,3,3] and 2) [7,8,9].  I could not figure out how to do it.

Many thanks.

Ed

## Is there an improvement as far as speed and memory...

Hello

I have used Groebner[UnivariatePolynomial] extensively on my procedures and I wonder whether there is an improvement in speed and memory use in Maple 2020 in relation to the version I am currently using, that is, Maple 2017.

Many thanks.

Ed

## Overflow? An abrupt in a plot suppose to be smooth...

I am doing this plot

loglogplot((.45*exp(-0.5e-1*t)+.1*exp(-.1*t))/exp(-0.5e-1*t), t = 1.4*10^4 .. 1.52*10^4);

and I got this weird abrupt change at some point: (please see the attached maple file)

1.mw

I guess it is due to how Maple implement those very large/small numbers.. Any thoughts?

## How to Plot a graph from O+ rather than fro -numbe...

Sort of revising fourier. I have a graph  however it gives result from -2pi to + 2pi. there must be a comand to modify plot to go from 0 to 2pi can someone give me a clue.

Rick

## Graph Theory graph cosmetics...

I have a graph with 267 nodes and 727 edges. I am trying to produce an eligible visualization of my graph but I'm getting a very crowded network.

Code:

with(GraphTheory);
DrawGraph(Graph(M1), style = spring, symbolsize = 10, scaling = unconstrained);

I have attatched the a JPEG file to my question to show what it looks like. I would like to space out the nodes with a more zoomed out view. How would I go about this?

## How do I compute a definite integral of a specifi...

Hello everyone .

I asked Maple to compute a definite integral of a function, numerically. Unfortunately it does not give me any values . I briefly explain what I did.

As you can see in the picture first I define a real valued function BW_dilog(x) (with complex domain), where the function dilog  already exists in maple. Then I defined another function, V, (with real domain and codomain ). Now I need the approximate value of the bi integral of V, on a triangle. The Maple file is attached.

I would be grateful if any one could help me.

## Assignment by address versus by value...

I initialized a variable name using another variable name and := . I thought that Maple would assign the value, but I soon learned by debug that the address was assigned. This led to temporary problems.

Where can I learn the rules that Maple follows for assignment by value or address ?? Do I always have to initialize with a real number, like 0, to be safe ??

Thanks.

Mike Graber

## How to preserve the order when extracting the coef...

Hello (again)

I thought I won't need help with that type of question but I came across an example that says otherwise.  Here it is

```vars:=[x,y,z];

model7 := [x*(-RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)-5/4)+y*alpha[1, 2]-33/(32*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)), x*z*alpha[2, 6]+y*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561), x^2*(17*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)+17)/(alpha[1, 2]*alpha[2, 6])-17*x*y/alpha[2, 6]+2*z*x-z-(163/32+RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)^2+5*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)*(1/4))/(alpha[1, 2]*alpha[2, 6])]
```

then I issued the command

```map(w->coeffs(w,vars),model7);
```

to get

`[-33/(32*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)), -RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)-5/4, alpha[1, 2], RootOf(64*_Z^3+80*_Z^2+1104*_Z+561), alpha[2, 6], -(163/32+RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)^2+5*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)*(1/4))/(alpha[1, 2]*alpha[2, 6]), -1, (17*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)+17)/(alpha[1, 2]*alpha[2, 6]), -17/alpha[2, 6], 2]`

clearly the order does not follow model7's.

I have also tried

`[seq(coeffs(expand(model7[i]), indets(model7[i], suffixed({vars[]}))),i=1..nops(model7))];`

Is there a solution to it?

Many thanks (again)

Ed

## Maple Graph: Command to find the average path leng...

I would like to analyse the graph I made and I cannot seem to find any command that gives me the average path length of an unweighted graph, is it perhaps referred as a different command? As I have tried searching Mean path length, distance and other derivatives with no useful result.

## How to list only real solutions when there are oth...

Hello

I have the following set of coefficients

`coef7 := [-1, 2, alpha[1, 2], alpha[2, 6], (17*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)+17)/(alpha[1, 2]*alpha[2, 6]), -17/alpha[2, 6], -33/(32*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)), -(163/32+RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)^2+5*RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)*(1/4))/(alpha[1, 2]*alpha[2, 6]), -RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)-5/4, RootOf(64*_Z^3+80*_Z^2+1104*_Z+561)]`

Considering that alpha[1,2] and alpha[2,6] are always real, how can I extract only the real solution from coef7?

Many thanks.

Ed

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